The invention relates to communications of telephony control signaling over data networks.
Traditionally, telephone calls are switched through a public switched telephone network (PSTN), which includes switching systems, circuits to carry voice and control signaling, telephone units, and other devices. Control signaling is exchanged to establish, maintain, and terminate calls over the PSTN. Control signaling can be communicated either in-band or out-of-band. In-band signaling is carried over the same circuits that carry voice during the call session. Out-of-band signaling uses a separate network to carry the control signaling. One widely used out-of-band signaling system is the Common Channel Signaling System No. 7 (SS7), which provides a separate signaling network to carry control signaling. Out-of-band signaling allows quicker setup of a call session and enables the ability to provide additional services, such as credit-card authorization, cellular phone roaming, and other services.
An SS7 system allows signaling data (e.g., data associated with call setup, billing, authentication, and so forth) to be exchanged between telephone switches (both wireline and wireless) and other telephony elements. The SS7 architecture includes several network nodes, including service switching points (SSPs), signal transfer points (STPs), and service control points (SCPs). SSPs are switches (such as those located at central offices) that originate, terminate, or tandem calls in response to call requests from a user or a local end office. The SSPs are linked by links to STPs, which are network nodes that act as hubs for routing signaling messages. An STP may perform global title translation, a procedure by which the destination signaling point is determined from digits present in the signaling message (e.g., the dialed telephone number, calling card number, or subscriber mobile identification number). The SCPs, also coupled by links to the STPs, include databases containing circuit, routing, and customer information.
Conventionally, the links among the various signaling nodes in the SS7 network include trunks (dedicated for carrying telephony control signaling) that are implemented with T1 spans (for relatively high bandwidth switches) or analog modem connections (for relatively low traffic switches). T1 spans are high-speed digital carrier links offering up to 1.544 megabits per second transfer rates.
Increased usage of the features offered by SS7 networks has created a need for a greater number of SS7 links between network nodes to carry control signaling between the network nodes. A predetermined amount of reserve capacity is provided in each SS7 link between network nodes. As bandwidth usage encroaches into such reserve capacity, additional capacity (e.g., additional SS7 links) may be added to the link between SS7 network nodes. Thus, for example, as more subscriber units are added to an SSP, the increase in call traffic may lead to a need for more capacity in the SS7 linkset between that SSP and the STPs to which the SSP is coupled.
T1 spans, however, are relatively expensive. Thus, adding T1 spans to expand capacity can be costly, especially for smaller switching points that support a relatively small amount of traffic and thus have either a small number of T1 spans or use relatively low-speed modem connections.
A need thus exists for methods and systems that enable communications of control signaling associated with telephony calls at reduced costs.
In general, according to one embodiment, a method of communicating control signaling messages in a telephony communications system having a plurality of nodes coupled by channels includes providing, in a node coupled to a channel having a first type link and a second type link, a first interface to the first type link and a second interface to the second type link. One of the first and second type links is selected to route a control signaling message to manage a call in the telephony communications system. The control signaling message is communicated over the selected link.
Some embodiments of the invention may provide one or more of the following advantages. A lower cost link may be employed for the communication of telephony control signaling. Incremental capacity may be added to an existing telephony network by using an existing data network such as the Internet. By providing two types of links for some nodes, redundancy is provided in case of link failure.
Other features and advantages will become apparent from the following description and from the claims.